Step 1

Bring the water and salt to a boil in a large, wide pot (such as a Dutch oven) over medium-high heat. Add the pasta and cook according to package directions, stirring occasionally, until tender. Do not drain the pasta.

Step 2

Reduce the heat to low. Add the shredded cheese, cream cheese, Parmesan, and mustard. Stir until all the cheeses are melted and the sauce is creamy. If the sauce is very thick, add water or milk a few tablespoons at a time until the desired consistency is reached. Taste and season with salt as needed. Serve immediately.